Advances in biotechnology have resulted in the development of a large number of novel therapeutic agents and methods for their use. Cytokines, polypeptides released by cells that act as mediators of a wide variety of physiological processes are particularly promising class of these novel therapeutic agents. Therapeutic methodologies employing cytokines are currently used to treat a variety of different pathological conditions including cancers as well as viral infections.
Cytokines are pleiotropic and modulate a wide variety of cellular activities. In therapeutic regimens, the effects of cytokines may not be restricted to diseased tissue but can also manifest in normal, healthy cells as well. As a result, undesirable side effects can arise during cytokine therapy, particularly when high doses are required. For example, administration of cytokines can lead to myelosuppression resulting in reduced red blood cell, white blood cell and platelet levels. Doses of cytokines can also give rise to flu-like symptoms (e.g., fever, fatigue, headaches and chills), gastrointestinal disorders (e.g., anorexia, nausea and diarrhea), dizziness and coughing. Consequently, there is a need in the art for a better understanding of the mechanisms of cytokine action and regulation so that new therapeutic methods can be developed and precisely tailored to optimize a therapeutic response while concurrently minimizing unwanted side effects.
Recently, a number of studies have focused on the mechanisms by which cytokine actions are negatively regulated by polypeptides know as “suppressors of cytokine signalling” (SOCS). Suppressors of cytokine signalling are a family of intracellular molecules including at least eight members, SOCS 1 to SOCS7 and cytokine inducible SH2-containing protein (CIS). SOCS polypeptides have been detected in various tissues and are produced in response to a large number of different cytokines. SOCS regulate the magnitude and duration of responses triggered by cytokines by inhibiting their signal transduction pathway in a classical negative feedback loop. For example, a variety of cytokines including interferons induce the expression of SOCS 1 and SOCS 3 proteins. These SOCS proteins then inhibit the activities of the cytokines that induced their expression. For articles discussing SOCS polypeptides and their mechanism of action, see, e.g. Song et al., Journal of Biological Chemistry, 273(53): 35056 (1998) Alexander et al., J. Leukocyte Biology 66: 588 (1999); Yasukawa et al., Annual Review of Immunology 18: 143-164 (2000); Chen et al., Immunity 13: 287 (2000); Nicola et al., Experimental Hematology 28: 1105 (2000); Fujimoto et al., International Immunology, 14911): 1343-1350 (2002); Crespo et al., Eur. J. Immunol. 32: 710-719 (2002); Chong et al., Diabetes 50: 2744-2751 (2001); O'keefe et al., Journal of Immunology, 166: 2260-2269 (2001); Cornish et al., Journal of Immunology, 170: 878-886 (2003); Dickensheets et al., P.N.A.S. 96: 10800-10805 (1999); Cottet et al., Journal of Biological Chemistry, 276(28): 25862-25870 (2001) and Federici et al., Journal of Immunology 168: 434 (2002), the contents of all of which are incorporated herein by reference.
At the molecular level, SOCS polypeptides bind directly to the catalytic domains of Janus kinase Oak) proteins within the cytokine receptor complex and act to impede the recruitment and phosphorylation and activation of downstream polypeptide efforts of cytokine signalling known as “signal transducers and activator of transcription” (STATs) (see, e.g. Gadina et al., Curr. Opin. Immunol. 13: 363 (2001)). The induction of SOCS by cytokines and negative regulation of cytokine signaling by SOCS have been documented in a variety of cell types (see, e.g. Sakamoto et al., Blood 92: 1668 (1998); Song et al., Journal of Biological Chemistry, 273(53): 35056 (1998); and Alexander et al., J. Leukocyte Biology 66: 588 (1999)). SOCS 1 inhibits interferon signaling by binding as a psuedosubstrate to Jak1 and Jak2, which are associated, respectively, with the IFN-R subunits. Thus disabled Jak1 and Jak2 cannot mediated STAT phosphorylation, which is necessary for the activation of γ-activated sequences (GAS) in the promoters of target genes (see, e.g. Gadina et al., Curt. Opin. Immunol. 13: 363 (2001); Yasukawa et al., Annual Review of Immunology 18: 143 (2000); and Stark et al., Annu. Rev. Biochem. 67: 227 (1998)). SOCS 3 also represses signalling induced by cytokines by similarly inhibiting STAT activation through binding to Jak kinases (see, e.g. Song et al., Journal of Biological Chemistry, 273(53): 35056 (1998)).
As noted above, the specific physiological processes associated with cytokine signalling are slowly being elucidated. In view of the current limited understanding of these processes however, medical practitioners are left to empirically determine optimal cytokine dosages and means of administration through trial and error. Unfortunately this results in less than optimal therapeutic regimens that, for example, exhibit a number of undesirable side effects which can compromise the therapeutic usefulness of such agents. Consequently, there is a need in the art for an understanding of the physiological mechanisms of cytokine action and regulation so that therapeutic methods that take these mechanisms into account can be developed. This information will allow medical personnel to design optimized therapeutic regimens that use cytokines in the treatment of various disease states. The invention disclosed herein meets this need.